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Amanda E. Smith,¹ Krassimira Hristova,¹ Isaac Wood,¹ Doug M. Mackay,¹ Ernie Lory,² Dale Lorenzana,² and Kate M. Scow¹

¹Department of Land, Air and Water Resources, University of California, Davis, California, USA; ²Port Hueneme Naval Construction Battalion Center, Oxnard, California, USA

Abstract
Widespread contamination of groundwater by methyl tertiary butyl ether (MTBE) has triggered the exploration of different technologies for in situ removal of the pollutant, including biostimulation of naturally occurring microbial communities or bioaugmentation with specific microbial strains known to biodegrade the oxygenate. After laboratory studies revealed that bacterial strain PM1 rapidly and completely biodegraded MTBE in groundwater sediments, the organism was tested in an in situ field study at Port Hueneme Naval Construction Battalion Center in Oxnard, California. Two pilot test plots (A and B) in groundwater located down-gradient from an MTBE source were intermittently sparged with pure oxygen. Plot B was also inoculated with strain PM1. MTBE concentrations up-gradient from plots A and B initially varied temporally from 1.5 to 6 mg MTBE/L. Six months after treatment began, MTBE concentrations in monitoring wells down-gradient from the injection bed decreased substantially in the shallow zone of the groundwater in plots A and B, thus even in the absence of the inoculated strain PM1. In the deeper zone, downstream MTBE concentrations also decreased in plot A and to a lesser extent in plot B. Difficulties in delivery of oxygen to the deeper zone of plot B, evidenced by low dissolved oxygen concentrations, were likely responsible for low rates of MTBE removal at that location. We measured the survival and movement of strain PM1 in groundwater samples using two methods for detection of DNA sequences specific to strain PM1: TaqMan quantitative polymerase chain reaction, and internal transcribed spacer region analysis. A naturally occurring bacterial strain with > 99% 16S rDNA sequence similarity to strain PM1 was detected in groundwater collected at various locations at Port Hueneme, including outside the plots where the organism was inoculated. Addition of oxygen to naturally occurring microbial populations was sufficient to stimulate MTBE removal at this site. In some cases, however, inoculation with an MTBE-degrading culture may be warranted. Key words: bioaugmentation, biodegradation, bioremediation, groundwater, in situ remediation, microbial ecology, MTBE, pollutants. Environ Health Perspect 113:317-322 (2005) . doi:10.1289/ehp.6939 available via http://dx.doi.org/ [Online 8 December 2004]

This article is based on a presentation at the conference "Bioremediation and Biodegradation: Current Advances in Reducing Toxicity, Exposure and Environmental Consequences" (http://www-apps.niehs.nih.gov/sbrp/bioremediation.html) held 9-12 June 2002 in Pacific Grove, California, and sponsored by the NIEHS Superfund Basic Research Program. The overall focus of this conference was on exploring the research interfaces of toxicity reduction, exposure assessment, and evaluation of environmental consequences in the context of using state-of-the-art approaches to bioremediation and biodegradation. The Superfund Basic Research Program has a legacy of supporting research conferences designed to integrate the broad spectrum of disciplines related to hazardous substances.

Address correspondence to K. Scow, Department of Land, Air and Water Resources, University of California, One Shields Ave., Davis, CA 95616 USA. Telephone: (530) 752-4632. Fax: (530) 752-1552. E-mail: kmscow@ucdavis.edu

We thank undergraduate students S. Adamson and B. Watanabe for their contributions. We are also grateful to the staff at Port Hueneme Naval Construction Battalion Center for their help in setting up the plots and sampling.

This publication was made possible by grant 5 P42 ES04699 from the National Institute of Environmental Health Sciences (NIEHS) , National Institutes of Health (NIH) . Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the NIEHS, NIH. Additional support was provided by the U.S. Environmental Protection Agency Center for Ecological Health Research, University of California (UC) Toxic Substances Program, American Petroleum Institute, Oxygenated Fuels Association, and the UC Water Resources Center.

The authors declare they have no competing financial interests.

Received 23 December 2003 ; accepted 30 June 2004.